The present invention is directed to the art of torque sensors and, more particularly, to a torque sensor for use in a power assist vehicle steering system.
Power assist steering systems are well known in the art and are frequently employed for use with automotive vehicles. The power assist is accomplished by applying a supplementary rotary force to a steering member. Such systems may be controlled in response to a driver""s applied torque to the vehicle""s steering wheel. Some of the known systems provide steering assist using hydraulic power, while other known systems use electric power.
U.S. Pat. No. 4,682,104 discloses an angular displacement sensor for use in detecting applied steering torque between an input shaft and an output shaft. The shafts are coaxially aligned with each other and rotatable relative to each other about a common axis. The sensor includes an input rotary transformer which includes a stationary primary winding and a rotary secondary winding. The secondary winding is mounted on one face of an annular disc which is, in turn, mounted on the input shaft for rotation therewith. A pair of detection disks, including a transmitter disk and a receiver disk, are axially displaced from the input rotary transformer. The opposing faces of these disks carry identical planar coils. The coils extend in the shape of spirally wound sectors which are coiled alternately in opposing directions and which coaxially surround the common axis of the input and output shafts. An AC voltage applied to the primary winding of the input rotary transformer is applied to the planar coils on the transmitter disk. This causes a voltage to be induced in the planar coils mounted on the receiver disk. An output rotary transformer having a primary winding coaxially surrounds the output shaft. The output transformer includes a stationary secondary winding on another disk axially spaced from the primary winding of the output transformer. An output signal, which varies with angular deviation between the input and output shafts, is provided by the output transformer.
U.S. Pat. No. 5,442,956 discloses a torque sensor for a power assist steering system which is similar to the sensor of U.S. Pat. No. 4,682,104, but which does not employ a transmitter or receiver disk carrying planar coils wound alternately in opposing directions. Further, the torque sensor includes first and second coils wound on the receiver disk which are connected with first and second output rotary transformers, respectively.
The present invention is a torque sensor for a power assist steering system for sensing applied torque between relatively rotatable input and output shafts which are connected by a torsion element. The torque sensor comprises a rotary input transformer for providing an input signal and a rotary transmitter connected for rotation with the input shaft. The rotary transmitter has a radially extending transmitter face divided into a plurality of transmitter pole segments by a plurality of radially extending slots. The rotary transmitter includes a transmitter coil electrically connected with the rotary input transformer. The transmitter coil completely encircles each of the transmitter pole segments individually and has two sections disposed in each of the plurality of slots. A rotary receiver is axially spaced from the rotary transmitter and is connected for rotation with the output shaft. The rotary receiver includes at least one receiver coil. A rotary output transformer for providing an output signal is electrically connected with the at least one receiver coil.
In accordance with one aspect of the invention, the rotary receiver has a radially extending receiver face divided into a plurality of receiver pole segments by a plurality of radially extending receiver slots. The plurality of receiver pole segments comprises alternating first and second receiver pole segment pairs. Each of the first and second receiver pole segment pairs comprises an adjacent pair of the receiver pole segments. Each of the first receiver pole segment pairs is disposed circumferentially between two of the second receiver pole segment pairs and is separated from the second receiver pole segment pairs by a first group of the plurality of receiver slots in the receiver face. A second group of the plurality of receiver slots in the receiver face extends between each of the adjacent pairs of the receiver pole segments in each of the first and second receiver pole segment pairs.
The rotary receiver includes a first receiver coil and a second receiver coil. The first receiver coil completely encircles each of the first receiver pole segment pairs and has two sections disposed in each of first group of receiver slots separating the first and second receiver pole segment pairs. The second receiver coil completely encircles each of a plurality of combined receiver pole segment pairs comprising one of the first receiver pole segment pairs and an adjacently disposed one of the second receiver pole segment pairs. The second receiver coil has two sections disposed in each of the second group of receiver slots extending between each of the adjacent pairs of the receiver pole segments in each of the first and second receiver pole segment pairs. A first rotary output transformer is electrically connected with the first receiver coil and a second rotary output transformer is electrically connected with the second receiver coil.